Collapsible ladders are known in which the stiles are formed of telescopically collapsible tubes and each rung is secured to a section of each stile. Each rung is formed with retractable pins at its opposite ends that engage in holes in the stiles to prevent the ladder from collapsing when a person is standing on one of the rungs. Manually operable levers or ring-pulls are provided to retract the pins, to allow the ladder to be collapsed one rung at a time. A disadvantage of such a ladder is that it is cumbersome and time consuming to collapse.
To overcome this disadvantage, a ladder has been proposed in EP 0527766 that is designed to collapse automatically from the bottom rung up. To collapse the ladder, pins of the lowermost rung are disengaged from the holes in the stiles to cause the whole of the ladder to drop by the height of one rung. As the lowermost rung contacts the rung above it, it releases the pins of the latter rung, causing the ladder to drop by a further rung height. This process is repeated until the whole ladder has been reduced to its minimum size.
It has further been proposed to use a ladder of the type described in EP 0527766 as a loft ladder. In this case, the top rung is pivotably attached to a rafter in the loft and a suitable stop is provided to support the weight of the ladder. For example, the stop may be part of a frame secured to a hatch door affording access to the loft.
When raised off its support, the ladder extends automatically under the weight of the ladder sections and the rungs lock into place. To collapse the ladder, the pins of the lowermost rung are disengaged from the stiles and as the lowermost rung is raised manually it disengages the pins of the next rung. Once again, continued raising of the bottom end of the ladder causes automatic release of all the stile sections one rung at a time, until the ladder is again small enough to be stowed in the loft.
Loft ladders need to be sized to suit the ceiling height and this may vary from one installation to another. The maximum height of the ladder may be varied by providing a greater or lesser number of rungs but the height between rungs is fixed and on some occasions the desired height may not be a whole number multiple of the distance between rungs.
To allow a ladder to be installed to suit differing ceiling heights, the present applicants have considered making the uppermost section of each stile rotatable relative to the section connected to the uppermost rung of the ladder and to form pin receiving holes in the uppermost section of each stile that are circumferentially and axially offset from one another.
The pins of the uppermost rung of the ladder will engage within the first holes in the uppermost stiles when the ladder is lowered. If the uppermost stile sections have holes that are circumferentially and axially staggered, it is possible during installation to set the effective length of the uppermost stile sections by rotating them, this having the effect of varying the distance travelled by the uppermost rung before its pins encounter holes in the stiles.
A loft ladder constructed in this manner suffers, however, from a problem in that if the uppermost rung is still in contact with the rung beneath it as it slides relative to the uppermost sections of the stiles, its pins will be in their retracted position, and will not engage with any of the holes in the uppermost stile sections, the upper ends of which are secured to the loft. The entire ladder therefore risks separating from the uppermost stile sections.